Improvement in power added efficiency (PAE) of a radio frequency amplifier circuit directly relates to reduction in power consumption of a device. Accordingly, the PAE is a very important property. In a high-output amplifier circuit, supplied power is converted into heat due to power consumption and a low PAE. This makes a heat-release design be difficult and decreases reliability of a device.
Conventionally, in order to cause the radio frequency amplifier circuit to operate at high efficiency, a device which includes a class-F circuit and an inverse class-F circuit has been generally used. Accordingly, mechanisms of these high efficiency circuits are known. In the amplifier circuit, power loss causes the efficiency to decrease. In order to prevent this, it is necessary to adjust a voltage/current waveform at an output so as to form an optimal waveform. To be specific, it is required to reduce an area where a voltage waveform and a current waveform overlap. For example, when a transistor included in the amplifier circuit is biased to a class-B operation, only a fundamental and even harmonics exist in an output current waveform. Thus, to reduce the aforementioned area, it is sufficient to set the output voltage waveform to include only the fundamental and odd harmonics. In order to achieve the above, if the even harmonics are set to be in a short-circuited state and the odd harmonics are set to be in an open state when viewed from an output of the transistor, the efficiency reaches 100% theoretically. This is the class-F circuit. Conversely, the inverse class-F circuit is such that the even harmonics are in the open state and the odd harmonics are in the short-circuited state. The class-F circuit and the inverse class-F circuit are selectively used depending on an on-resistance and a bias condition of the transistor to be used.
Patent Literature 1 discloses a high-efficiency radio frequency amplifier circuit including the conventional class-F circuit.
FIG. 7A is an analogous circuit which shows a configuration of a conventional radio frequency amplifier circuit. The radio frequency amplifier circuit includes, as shown in FIG. 7A, a transistor 701, an inductor 702A having a lumped parameter element, a capacitor 702B, fundamental matching inductors 703A and 703B each of which has a lumped parameter element, and fundamental matching capacitor 703C having a lumped parameter element. In the circuit, a secondary harmonic processing circuit 702 including the inductor 702A and the capacitor 702B is connected to an output terminal of the transistor 701 in parallel, the fundamental matching inductors 703A and 703B are connected to the output terminal of the transistor 701 in series, and the fundamental matching capacitor 703C is connected between the fundamental matching inductors 703A and 703B in parallel. The above circuit configuration performs a secondary harmonic processing and improves the efficiency. Specifically, the inductor 702A and the capacitor 702B are set so that the secondary harmonic processing circuit 702 serving as a series resonant circuit resonates at a frequency twice as high as the fundamental, causing an impedance of the secondary harmonic processing circuit 702 to be 0 at a secondary harmonic. Accordingly, the secondary harmonic processing circuit 702 is in a short-circuited state for the output terminal of the transistor 701. Furthermore, the fundamental matching circuit 703 including the fundamental matching inductors 703A and 703B and the fundamental matching capacitor 703C is connected to the transistor 701.
FIG. 7B is a diagram which shows an example of a layout for achieving the conventional radio frequency amplifier circuit shown in FIG. 7A. In order to achieve high output in the radio frequency amplifier circuit, low-output transistors are typically connected in parallel to obtain the high output. As shown in FIG. 7B, a plurality of output terminals (drain terminals) of the transistor 701 which are connected in parallel, and a capacitor 702B are connected by a plurality of wires corresponding to the respective inductors 702A included in the secondary harmonic processing circuit 702. Meanwhile, the output terminals of the transistor 701 and the capacitor 703C used for fundamental matching are connected by a plurality of wires corresponding to the respective inductors 703A included in the fundamental matching circuit 703. In addition, wires corresponding to the respective inductors 703B are formed for connecting the output terminals of the transistor 701 to an external circuit 705. The capacitor 702B and the fundamental matching capacitor 703C are patterned on a dielectric substrate 704.
Patent Literature 2 discloses a radio frequency amplifier circuit used for causing harmonic reflection quantity to relatively increase with respect to a fundamental. In the radio frequency circuit, a transistor is divided in units of cells to operate in parallel. Each of the divided transistor cells is connected, in an output-terminal side thereof, to a tertiary harmonic processing circuit, a secondary harmonic processing circuit, and an output-side fundamental matching in series. The plurality of output signal lines connected in series are combined into one in a power combining circuit. This achieves high efficiency in operation of a radio frequency amplifier circuit while variation of the harmonic load for each of the transistors is suppressed, in comparison with a case where the harmonic processing circuit is formed without dividing the transistor.